Diaphragm



Mamh 19, 19290 L KlMBALL 1,705,771

DIAPHRAGM Filed July 1925 Patented Mar. 19, 1929.

UNITED STATES PATENT OFFICE,

IRVING KIMBALL, OF BBOOKLINE, MASSACHUSETTS, ASSIGNOB TO GLOBE TECH- NOLIAN CORPORATION, OF BOSTON, MASSACHUSETTS, A CORPORATION OF MASSA- onusn'r'rs.

DIAPHRAGM.

Application filed July 6,

This invention relates to a diaphragm for use in sound reproducing apparatus, and has for an object to provide a novel and superior construction of diaphragm, which is particularly useful in place of the ordinary steel, mica or rubber diaphragms used in such apparatus, and by which sound and particularly music, of superior tone and quality vmay be reproduced.

With this object in view, the. invention consists in the diaphragm hereirgzfter de scribed and particularly defined in the claims at the end of this specification.

In the drawing illustrating the preferred embodiment of the invention, Figure 1 illustrates more or less diagramatically a loud speaker unit of the balanced armature type at present upon the market, and in which the present construction of diaphragm is embodied; Fig. 2 is an exploded View of the laminations comprising'the present diaphragm; and Fig. 3 is a sectional View illustrating the usual form of phonographic reproducer unit with which the present diaphragm may be used with advantage. In the reproduction of sound by diaphragm vibration, and particularly of music, as in phonographic and radio work, the distortion of the sound accompanying the performance of the different forms of the reproducing apparatus at present upon the market is noticeable particularly to the expert and detracts from the accuracy with which the original sound or music may be reproduced in details of quality and tone. I have determined that a large amount of this distortion is caused by the natural period of vibration in the diaphragm itself, and that as a consequence of this vibration inherent in the diaphragm itself because of its construction, the sound or musical re roduction is accompanied by distortion w ich I believe to be the cause of the production of false harmonics or over-tones.

'In accordance with the present invention a diaphragm is constructed to eliminate, to a large extent, this objectionable distortion. in tone, and the inherent vibration resulting from the natural period of vibration in the diaphragm itself, and the consequent production of these objectionable false overtones and false harmonics, and for this purpose I have discovered that a laminated structure involving opposing sheets of rub- 1925. Serial N0.*41,626.

her or rubber composition applied and ad boring to the opposite surfaces of a diaphragm core, and which maybe covered by fibrous-material in sheet form, possesses the property of eliminating to a large extent the production of these objectionable false harmonics and false over-tones whenthe diaphragm is used in sound reproducing apparatus in radio, telephone and phono graphic work, so that the tone produced is that of the original voice or music.

Referring to the drawing, 10 represents a diaphragm embodying the present invention, and which comprises a laminated structure formed of a plurality of individual sheets of different material, and which is diagrammatically illustrated in an exploded position in Fig. 2. Referring to Fig. 2, the diaphragm preferably comprises a steel core 12, although mica or rubber diaphragms of' a relatively stiff nature may,

for certain purposes, be found suitable. The

steel core 12 is preferably of the construction of the ordinary steel diaphragm used in loud speaker units in radio work, and the core 12 is, in accordance with the present invention, provided upon its opposite surfaces with relatively thin sheets 13, 14 of rubber or rubber composition, and preferably of unvulcanized rubber, and the rubber sheets 13, 14 are preferably vulcanized or cemented upon the steel diaphragm 12, as will be described. The outer surfaces of the rubber sheets 13, 14, may, and preferably will be, covered with thin sheets of fibrous material, and I have found that excellent results may be secured by ing one sheet 15 of paper, the pores 0 which may be filled with a suitable lacquer of any usual or preferred composition, to prevent it from absorbing moisture, and a'second sheet 16 of chamois. In applying the rubber sheets 13, 14 and the fibrous sheets 15 and 16, I prefer to form the sheets of a shape corresponding to the central core or diaphragm 12, and to assemble the sheets under heat and pressure, by which the rub,- ber sheets 13, 14; are caused to melt to a certain degree sufficient to cause them to firmly adhere to the surfaces of the sheet 12, and preferably to become vulcanized and to adherently secure the fibrous sheets 1:1, 16 tothe core 12, producin a laminated structure in which the di erent laminaprovid- I tions are securely altixed to one another, and enabling the diaphragm to function in the desired manner, but Without the objectionable production of false harmonics and over-tones above referred to.

The rubber layers 13, it appear to have the effect of preventing the laminated diaphragm from producing the false over-tones and at the same time do not detract from the etliciency of the diaphragm, so that when used for radio reception in a loud speaker unit, the diaphragm functions to faithfully reproduce the original music or voice.

llor radio Work, and particularly as the diaphragm of loud speaker units such as is illustrated diagrammatically in 1, the present diaphragm is preferably arranged With the chamois 16 upon the inside, and l have found that by so arranging the chamois sheet 16, the vibrations produced during the operation of the unit are caused to pass to the amplitying horn or member of the unit Without any distortion resulting from echoes or other causes, and as a result the tone producedis deepened Without blurring or distortion, and is a practically perfect repro; duction of the original sound or music.

in Fig. 1 a portion of a loud speaker unit for radio reception is shown with portions of the electromagnetic mechanism for its actuation. The details oil the latter form of themselves no part of the present inven tion, and may comprise any of the known forms now upon the market. The illustr ted form is the WQllrlZilOWll balanced armature .ype wherein an armature 3O pivoted. at is oscillated. up and down and throw h in t connection 33 operates in the u. .ianner to cause the diaphragm 10 to virate in accordance with the music or voice eing; reproduced.

Similarly, the present construction oil laminated diaphragm is particularly as l L :for phonographic vvorlr and, illustrated in 3, the diaphragm unit comprises the usual casing 40 Within which the present diaphragm 10 is secured in the usual manner by a clamping ring with the ehamois layer 16 oil the diaphragm onthe inside, or in a position adjacent to the socket into which the end of: the tone arm i l or the phonograph tits. The usual form of styli' L6 is connected by the List at the center of the di the stylus travels upon the record, the vibration imparted to the diaphragm 10 causes the reproduction ot the sound or music in the usual manner, except that he laminated construction oi diaphragm alcove describe avoids the production, or reduce to a minimum the production, of false hen weaver accompanied the operation of the usual form of diaphragm, and causes distortion, harshness and objectionable reproduction of the original voices or music.

While the preferred embodiment has been illustrated and described, it is to be understood that the invention may be embodied in other forms Within the scope of the fol lowing claims.

Having thus described the invention, What is claimed is:

l. A diaphragm for sound reproducing apparatus comprising a laminated structure having a relatively stiff circular central core, solid layers of thin sheet rubber upon opposite surfaces thereof, adhesively alhaed to the core, and layers of fibrous material covering said rubber layers and adhesively secured thereto.

2. A diaphragm for sound reproducing apparatus comprising a laminated structure having; five layers of equal and corr-- posed of a steel core, rubber layers upon opposite surfaces thereof and adhesively secured thereto, a fibrous layer covering one of said rubber la ers, Chamois layer covering the other of said rubber." layers.

23. A diaphragm for sound reproducing apparatus comprising a laminated structure provided with an outer layer of chamois.

4:. A diaphragm for sound reproducing apparatus comprising a core provided with material on the surraees erect or reduo ing the tendency of tie diaphragm to vibrate at a natural period, compi 'sing relatively thin sheets of rubber adhes aliizzed to and cov ring said surfaces 0.. the :ore, said core of such dimer ions as to completely separate the two ruober sheets.

In asounc. reproduci i apparatus having provision for conducting; sound waves to an amplifier, damir t daphragm co; prisms" a core and on material at least one and "which one is adjacei.

in a sound reproducing :ing provision conducting sour prising steel core With COVOl'lfig layers at one side and chamois at the otl er side each being secured to the core by an interposed layeit' oi sheet rubber, and having said chaniois layer facing the amplifier. k

laminated dis.

.1- lift 1d Wax-cs to amplifier, a laminated diaphragm coinethod oi incl p rns which comprises assembling a dish. unvulcanized rubber against each of a circular core and a dish of fibrous terial against each dislr. of rubber, then up plyingheat and pressure to cause adherence rll the layers through. vulce of the oer 

